Conventional golf balls can be divided into two general classes: solid and wound. Solid golf balls include one-piece, two-piece (i.e., single layer core and single layer cover), and multi-layer (i.e., solid core of one or more layers and/or a cover of one or more layers) golf balls. Wound golf balls typically include a solid, hollow, or fluid-filled center, surrounded by a tensioned elastomeric material, and a cover.
Golf ball core and cover layers are typically constructed with polymer compositions including, for example, polybutadiene rubber, polyurethanes, polyamides, ionomers, and blends thereof. Playing characteristics of golf balls, such as spin, feel, CoR and compression can be tailored by varying the properties of the golf ball materials and/or adding additional golf ball layers such as at least one intermediate layer disposed between the cover and the core. Intermediate layers can be of solid construction, and have also been formed of a tensioned elastomeric winding. The difference in play characteristics resulting from these different types of constructions can be quite significant.
Ionomers, particularly ethylene-based ionomers, are a preferred group of polymers for golf ball layers because of their toughness, durability, and wide range of hardness values. Ionomers initially became popular golf ball cover materials due to their excellent impact resistance and their thermaplasticity, which permits the material to be economically applied via injection or compression molding techniques.
Specifically, highly neutralized acid polymers or HNPs, are beneficial. For example, U.S. Patent Application Publication No. 2003/0130434, the entire disclosure of which is hereby incorporated herein by reference, discloses melt-processible, highly-neutralized ethylene acid copolymers and processes for making them by incorporating an aliphatic, mono-functional organic acid in the acid copolymer and then neutralizing greater than 90% of all the acid groups present. Also, in U.S. Patent Application Publication No. 2005/0148725, the entire disclosure of which is hereby incorporated herein by reference, highly-resilient thermoplastic compositions comprising (a) an acid copolymer, (b) a salt of an organic acid; (c) a thermoplastic resin; (d) a cation source; and (e) optionally, a filler are disclosed. The reference also discloses one-piece, two-piece, three-piece, and multi-layered golf balls comprising such highly-resilient thermoplastic compositions.
However, there is a need in the golf ball industry to develop and refine highly neutralized acid polymer materials that display excellent resilience at given compressions and with soft feel. Golf balls of the present invention and the methods of making same address and solve this need.